The invention relates to a gravure printing unit for a rotary press, with a plate cylinder supplied with printing ink from a printing unit and an impression roller, which lies essentially at right angles to the plate cylinder and forms a roller gap with it. When the rotary press is running, sheet material that is to be printed is passed through the roller gap, taking up printing ink from the peripheral surface of the plate cylinder. At the same time, the plate cylinder rotates in a specified direction opposite to that of the impression roller and its rotational movement is composed of a leading, rotating sector from the inking unit to the roller gap and a hailing rotating sector from the roller gap to the inking unit.
In the case of such gravure printing units, the printing sites of the plate cylinder forming the printing forme are recessed in the manner characteristic for gravure printing in the form of gravure cells of optimally different depth and/or area for holding the printing ink. The excess ink of the plate cylinder, supplied with printing ink from the inking unit, usually by being dipped in an ink fountain, is removed by a doctor blade or a similar stripping device. As the sheet of material, which is to be printed, is passed through the roller gap formed between the plate cylinder and the impression roller, the ink is sucked out of the gravure cells and transferred to the sheet. The leading rotating sector of the plate cylinder ends here. Since the gravure printing ink, aside from pigments, binders and fillers, contains volatile solvents, the tendency exists that the slight ink residues, which remain in the gravure cells when the ink is being transferred in the roller gap, dry out on the trailing rotating sector of the plate cylinder, before they reach the inking unit or the ink fountain on the trailing rotating sector, in order to be filled once again with printing ink there and returned on the leading rotating sector of the plate cylinder to the roller gap for transferring the printing image. This drying-out effect can vary depending on the composition of the ink and the construction of the gravure cells. The cumulative effect of such ink residues, which have dried out in the gravure cells, leads to a visible deterioration in the printing image produced because the ink absorption capacity of the gravure cells becomes increasingly less correspondingly.